Chemical looping reforming (CLR) technology is a clean and efficient fuel conversion process for direct hydrogen production by using solid metal oxides. Instead of the traditional use of steam or pure oxygen

solid metal oxides are typically used as oxygen carriers to convert carbonaceous fuel to syngas or CO2/H2O. The reduced oxygen carrier then reacts with the steam for directly generating H2

which is separated in situ with near zero energy consumption. Based on the need for different products and the different heat supply methods

both two-reactor and three-reactor CLR systems have been discussed

with a focus on the characteristics of oxygen carriers and reactor design. The Elingham diagram is used to compare the redox properties of various metal oxides

and to guide the selection of suitable oxygen carriers for direct hydrogen production. Recent oxygen carrier development is also discussed to investigate the strategies for improving H2 selectivity and yield. The gas solid contacting pattern should be carefully selected when designing CLR reactors with various kinds of feed fuels and target products.